When the Crown Jewels go missing from inside a locked room, Mac's spy skills are put to the test. How did the thief break in? Where did the jewels go? And will Mac be able to solve this locked-room mystery before the thief escapes? This mystery isn't just a whodunit... it's a howdunit! The action in this adventure is nonstop as Mac travels to an ancient Irish castle to solve the mystery. There, he encounters everything from killer king cobras to bizarre ice sculptures...and even a revenge plot dating back hundreds of years! Will you be able to solve the mystery before Mac does? Featuring historical facts masterfully woven throughout the plot, the second entry in the totally smart and side-splittingly funny New York Times bestselling series Mac B., Kid Spy shouldn't be missed!